(1) Field of the Invention
The present invention relates to emulsion polymerization emulsifiers, methods of preparing the emulsifiers and latex compositions comprising the novel emulsifiers. The present invention more particularly relates to novel emulsion polymerization emulsifiers described as the half vinyl esters of C.sub.21 -dicarboxylic acid of the formula ##STR2## wherein x and y are integers from 3 to 9, x and y together equal 12, one Z is COOH and the other Z is hydrogen.
(2) Description of the Prior Art
Emulsion polymerization is one of several methods for effecting the process of addition polymerization. The monomer is emulsified in a medium, generally water, with the aid of micelle generating substances, or emulsifying agents, such as soaps, alkyl sulfonates, etc. In addition to the monomer, water (as the continuous phase) and emulsifier, the process requires an initiator. Hydrogen peroxide and ammonium peroxysulfate are examples of such initiators.
One of the principal advantages of emulsion polymerization is the possibility of formation of a polymer of high molecular weight at a very high rate of polymerization. In this respect emulsion polymerization stands alone among techniques of free radical polymerization. Thus, this process has gained widespread commercial acceptance.
Meis and Werk, in U.S. Pat. No. 2,300,056 developed emulsifiers for emulsion polymerization from mixtures of (a) water soluble surface active emulsifying agents and (b) water soluble salts of unsaturated carboxylic acids the esters of which represent drying oils, particularly alkali metal salts.
Force, a co-inventor in this application, disclosed acid-catalyzed, formaldehyde-treated mixtures of tall oil fatty and resin acids as emulsion polymerization emulsifiers in U.S. Pat. No. 4,259,459. Also, in Emulsion Polymerisation, Theory and Practice (1975), at Chapter 7, Blackley discusses the use of various fatty acid soaps and rosin acid soaps as micelle generating substances. Of considerable concern, however, is the effect upon polymerization which may be caused by adventitious impurities in the fatty acid or rosin acid soap used, particularly soaps derived from unsaturated fatty acids. Wilson et al. reported in Industrial Engineering Chemistry (1948), Vol. 40, p. 530, that soaps derived from linoleic and linolenic acids retard the copolymerization of styrene and butadiene. Naturally, the emulsifier also should not disturb the physical properties of the polymer.
A major concern for producers and consumers of certain polymer products is the migration of emulsifier from the polymer. In some cases the result is merely a visual or aesthetic problem; in other cases, the result can be more dramatic, as with hoses for gasoline and other fuels. For those end uses where migration of emulsifier is of concern, two approaches can be taken to minimize problems: (1) washing the emulsifier from the latex before further converting operations or (2) polymerizing the emulsifier into the polymer so that the emulsifier is permanently bound.
The first approach is commonly used but results in increased cost due to added operational steps. The second approach is less commonly used because such emulsifiers typically are very expensive and have limited scope primarily due to low polymerization activity.
Greene et al., in "In Situ Polymerization of Surface-Active Agents on Latex Particles," in Journal of Colloid and Interface Science, Vol 32, p. 90 (1970), disclose the sodium salt of 9- (and 10-) acrylamidostearic acid as a polymerizable micelle generator for a 60/40 styrene-butadiene copolymer. It is reported that the in situ polymerized soap is more efficient in conferring mechanical stability than is an added monomeric soap, as long as the surface coverage exceeds 20%.
An object of the present invention, therefore, is to provide a novel latex composition from which, upon polymerization, the emulsion polymerization emulsifier will not migrate. A further object of this invention is to provide a polymerizable emulsifier for use in an emulsion polymerization process which, upon polymerization, will be permanently bound. Also, an object of this invention is to provide an emulsifier which neither inhibits polymerization nor adversely affects the polymer physical properties. A still further object of this invention is to provide a polymerizable emulsifier which is relatively inexpensive compared to known polymerizable emulsifiers.